The present invention relates to an automatic document feeder for use in image forming apparatus such as copying machines, and more particularly to the structure of an automatic document feeder adapted to automatically deliver a document, for example, from a copying position and discharge the document on reversal after the document has been used for copying.
Conventional automatic document feeders of the type mentioned include, for example, the one disclosed in Unexamined Japanese Utility Model Publication SHO 60-159757. This prior-art feeder will be described with reference to the schematic sectional view of FIG. 3. The illustrated automatic document feeder, which is indicated at 31, is placed on the body 32 of a copying machine the top portion only of which is shown. Indicated at 33 is a contact glass plate provided at the top of the machine body 32.
A roller 35 is disposed above a document tray 34. Feed rollers 36 and 37 are arranged downstream from these members. Provided downstream from the feed rollers 37 is a conveyor belt 39 reeved around a drive roller 38a and a driven roller 38b. The drive roller 38a is coupled to an unillustrated drive motor, by which the conveyor belt 39 is driven in the direction of arrow A. Documents on the tray 34 are sent out one by one from the uppermost position by the roller 35 and forwarded to the feed rollers 37 by the feed rollers 36. Each document is then fed onto the glass plate 33 by the feed rollers 37 and the conveyor belt 39.
Disposed downstream from the conveyor belt 39 is an assembly for reversing and discharging the document. More specifically, a transport roller 40 and an idle roller 41 in pressing contact therewith are provided downstream from the belt 39. A discharge roller 42 and an idle roller 43 in pressing contact therewith are arranged at a suitable position above the rollers 40, 41. The idle rollers 41, 43 are biased toward the transport roller 40 and the discharge roller 42 by springs 44, 45, respectively. Guide plates 47, 48 defining a document passage 46 are arranged between the rollers 40, 42. To transport the document efficiently, these guide plates 47, 48 are each in the form of a circular arc. Although not shown, the outer guide plate 47 is formed with ribs to ensure reduced friction. The belts indicated in broken lines are provided for driving the rollers 40, 42 as timed with the conveyor belt 39.
When a copying operation has been completed for the document placed on the glass plate 33, the document is sent as deflected slightly upward to the transport roller 40 by the conveyor belt 39, and transported through the passage 46 by the transport roller 40 and the idle roller 41 to the discharge roller 42, as generally reversed in the direction of its transport. In this way, the document is finally delivered onto an external discharge tray 51 by the discharge roller 42 and the idle roller 43. Thus, the feeder is adapted to reverse and discharge the document with the transport roller for handling the document before reversal, the discharge roller for handling the document after reversal and the smoothly curved document passage.
A device is also known which corresponds to the conventional automatic document feeder of FIG. 3 from which the transport roller 40 and the idle roller 41 are omitted to reduce the number of components and achieve a cost reduction.
The assignee of the present applicant has already proposed an automatic document feeder corresponding to the feeder of FIG. 3 from which the idle roller 43 is also omitted. The proposed feeder is adapted to discharge the document by the operation of a discharge roller 42 made of a relatively soft material such as sponge and ribs at the discharge portion so as to realize a further cost reduction (Japanese Patent Application SHO 63-249114).
With the first-mentioned feeder, the reversal discharge assembly includes a plurality of rollers, especially the transport roller, and therefore requires gears, etc. for the roller coupling mechanism and synchronized rotation of the roller. Further to ensure reliable transport of documents, the transport roller and the discharge roller are provided with idle rollers and springs for pressing the idle rollers into contact with these rollers. Consequently, the assembly is complex in construction, large-sized and costly.
In the case where the transport roller 40 and the idle roller 41 are omitted from the feeder of FIG. 3 or in the case where the idle roller 43 is also omitted along with these rollers, the document must be sent to the discharge roller 42 only with the transport force of the conveyor belt 39. In this case, moreover, the document delivered from the conveyor belt 39 needs to be reversed in the direction of transport and forwarded to the position where it is to be held between the discharge roller 42 and the ribs, so that the feeder is not always capable of transporting the document reliably only with the conveyor belt 39 but permits paper jam. This phenomenon occurs noticeably when the document is thick.